The present invention relates to an apparatus which is incorporated in a dual hydraulic brake system for a vehicle.
In automotive and other vehicles having dual hydraulic brake systems and disc-type brakes on the front wheels and drumtype brakes on the rear wheels, it is necessary to have the braking forces and torques be applied approximately simultaneously to the front and rear wheels. This prevents a dangerous skidding condition. It is also desirable in such systems to provide an indication to the vehicle operator of the occurrence of a failure of either the front or rear brakes.
Also, where a line of vehicles is being assembled, and a standard chassis, brake system, disc brake calipers, and the like are being utilized for all of the vehicles in the product line, it is necessary to provide a braking system which will have application for all the vehicles, regardless of their weight or the use to which they will be put. This problem becomes critical where the vehicles comprise trucks and the difference in vehicle weight from the lightest and smallest end of the product line to the heaviest and largest end is substantial. In such cases, if large caliper disc-type brakes are utilized on the front wheels, then it is necessary to limit their functioning and balance the braking forces between front and rear wheels so that undesirable and potentially dangerous high braking torques will not be produced in the lightest trucks. The present invention provides an apparatus for solving this problem and at the same time for prohibiting the application of the disc brakes on the front wheels until the drum-type brakes on the rear wheels are functioning and for providing a brake system failure warning indication.
Limiting the pressure applied to the front wheels on trucks and other heavy road vehicles does not create any conflict with the weight transfer which occurs during braking applications. On the smaller, lighter truck models, the large heavy-duty disc brakes provide more than sufficient braking torque and force on the front wheels. On the larger, heavier truck models, the additional weight of the truck itself provides sufficient weight to prevent the rear wheels from skidding. Further, if the truck is loaded to any extent, that load is generally centered over the rear axle and provides additional downward force on the rear wheels.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and claims taken in conjunction with the accompanying drawings.